Patent GB-1100922-A (GB)
Title: Improvements to aircraft braking systems
IPC: B64F1/02
Filed: 1965-01-27
Abstract: 1,100,922. Aircraft braking system. SOCIETE GRENOBLOISE D'ETUDES ET APPLICATIONS HYDRAULIQUES (SOGREAH), and SOCIETE FRANCAISE AERONAUTIQUE ET MARITIME (SOFRAM). 27 Jan., 1965 [29 Jan., 1964; 7 Feb., 1964; 29 Sept., 1964], No. 3640/65. Headings F2E and F2F. Apparatus for automatically braking an aircraft to a standstill on a runway comprises braking means operable to brake the aircraft, comparing means operable to compare a nominal value or factor representing a predetermined value of aircraft deceleration with the value of the true deceleration of the aircraft or a factor representing said true deceleration, such as the aircraft speed at a given aircraft position on the runway or vice versa, control means sensitive to the output of the comparing means and operable to control the braking so that the real deceleration tends to the desired value, whereby the braking distance remains substantially constant for variations in aircraft mass and landing speed. As shown, an aircraft 11 is braked by an arrester wire unreeling from a pair of drums 8, 8<SP>1</SP> each braked by a pair of hydrodynamic brakes 10, 10<SP>1</SP>. Since it is easier to measure the real or true angular acceleration of the guide pulley 12 than that of the aircraft, the actual deceleration of the pulley is measured by a decelerometer 14 and fed into comparator 18. Since this measured deceleration is a distorted value of the true aircraft deceleration which varies with the aircraft position along the runway, the desired value of aircraft deceleration 15 is converted to corresponding pulley angular acceleration according to aircraft position along the runway by a corrector 16, the converted desired acceleration being compared with the input of meter 14 in the comparator. The difference in inputs actuates a governor 19 to adjust the brakes as necessary. In a modification, Fig. 3 (not shown), the measured pulley deceleration is converted by means 20 to a value corresponding to the real aircraft deceleration and then compared with the desired value. As illustrated in Fig. 4 (not shown), the true aircraft deceleration may be obtained by utilizing a similar or geometrically scaled model. Another feature of the invention, Fig. 6 and 7 (not shown), comprises an hydrodynamic brake (25) having a balanced stator (26) consisting of an arm (28) maintained by a spring (27) acting between said arm and a nut (29) which is moved along a threaded spindle in dependence on the position of the aircraft along the runway. Since the rotational speed of the brake is dependent on aircraft speed, the position of the stator at any instant is dependent on both the aircraft speed and its position along the runway. Movement of the balance arm produced by these two inputs effects operation of control shutters (35) of an auxiliary high power hydrodynamic brake 31 to increase the braking as required. Figs. 7 and 8 (not shown), an insert strip of varying thickness is wound initially on the arrester cable drum of the previous embodiments with the arrester cable so that the effective cable drum radius decreases in the desired manner as the arrester cable is drawn off. Alternatively as illustrated in Fig. 9 (not shown), the arrester cable is wound on a drum having helicoidal steps or grooves to provide a variable radius drum.